The present invention relates to a filter for treating gases to remove undesirable components therefrom, especially from exhaust gases of engines, and particularly internal combustion engines, such as, for example, Diesel engines, and the like. The filter includes a filter body or element having a plurality of inlet and outlet channels, with the inlet channels being separated from the outlet channels by means of walls or partitions which define reaction chambers.
With respect to removal of, for example, soot and the like deleterious substances from exhaust gases, particularly in reference to Diesel engines, soot filters made of ceramic material are known. In such applications, the soot filter is generally positioned in the exhaust duct or pipe system of the internal combustion engine and downstream of the exhaust manifold.
The hot gases emanating from the engine flow into the inlet channels of the filter body or element, pass through the porous filter walls which surround the inlet channels, and they are subsequently emitted by means of the respective outlet channels.
Due to high temperature conditions, the soot, i.e., carbonaceous matter, is converted in the filter walls into gaseous matter and ash, and these are emitted together with the exhaust gas from the exhaust duct.
A particular detriment of ceramic filters resides in their particular porosity, especially the pore size distribution and the spherical pore configuration, which determines separation of soot but also limits soot separation. A substantial change of the porosity is precluded, however, by the special structural characteristics of the ceramic material.
Ceramic filters have other drawbacks. They are particularly sensitive to rapid changes in temperature, localized over-heating by exhaust gases due to poor thermal conductivity, and against shocks and blows or the like impact stresses. This means that the filter body must be exteriorly surrounded by a material which is protecting or insulating with respect to temperature and shock, generally stone wool, and this insulating material, in turn, is enclosed by a housing. Thus, the known soot filters occupy a considerable space and in consideration of oftentimes experienced limited space availability, problems are experienced in the engine compartment of a motor vehicle.
The drawbacks of ceramic filters are also apparent in any recycling, when such filters are coated with catalytically acting or active metals, such as, for example, platinum, rhodium, vanadium and palladium. These metals need then to be recovered with laborious methods during requisite recycling from the ceramic body. In addition, the serviceable life of such ceramic bodies is limited due to stresses, and this problem represents a considerable cost factor which needs to be addressed during manufacture and ultimate sale of such ceramic bodies.
Also known are exhaust gas catalysts which by catalytic action remove further deleterious components such as, for example, carbon monoxides, hydrocarbons, and nitric oxides from the exhaust gas. For this purpose one uses, for example, filters with coatings of platinum, rhodium, vanadium, and other catalytically acting materials. Such filters which are based on ceramic materials, however, are expensive and, furthermore, sensitive to operating conditions.